Mr Clegg told the Today programme he had expected the argument - "perhaps naively with hindsight" - would not have been one "waged by politicians sitting in radio and television studios".

Instead it has seen the deputy prime minister singled out as a reason to vote 'no' because of his decisions to renege on promises made before the 2010 general election.

"If this referendum has dramatised or amplified the fact this coalition government is composed of different parties, and the Liberal Democrats are the progressive party in this arrangement, I don't think that's a bad thing in the long-run," Mr Clegg said.

"The first phase of this coalition government, as we were taking really difficult decisions on the deficit and so on, required a collective discipline, but that over time inevitably the different character of these two parties would come out in the wash a bit more."

He suggested his Conservative party colleagues in government had sought to defend the current first-past-the-post system because they wanted to protect the system which benefits them the most.

"This is a party that has long believed in choice and competition in the economy and so forth," Mr Clegg added.

"I don't for the life of me understand why they now want to resist a simple change that would give people more choice."

Speaking on the same programme, prime minister David Cameron insisted he was "proud" of the Conservative 'no' campaign.

But he was careful to differentiate this from the wider 'no' campaign, which has faced accusations of outright lying from some quarters.

He said first-past-the-post was "simple", "fair" and "decisive", adding that "I believe it is fair for this reason: if you go to an alternative vote system you start counting some people's votes more than once".

The prime minister said the coalition government was functioning smoothly despite the tensions triggered by the alternative vote referendum.

"This was always going to be a difficult moment with the two parties on different sides of a referendum campaign," he said.

The emergency Cobra meeting taking place in the wake of Osama bin Laden's death demonstrated that Tories and the Lib Dems were able to continue working together "to keep the country safe from terrorism", however.

"We are being a very cohesive and strong government," Mr Cameron added.

Opinion polls suggest the prime minister is likely to emerge victorious after voting this Thursday.

Mr Clegg, who had backed proportional representation before the general election, hinted that another referendum could take place in a future parliament.

"This is not a stepping stone to perpetual Maoist revolution," he said.

"This is the choice we've got. It's the choice for this parliament during which this government is in power. What future parliaments do, of different parties perhaps, is entirely up to them."